On the seismic vulnerability of existing buildings; a case study of the city of Basel

In order to assess the seismic risk for Switzerland, and particularly for the city of Basel, the seismic vulnerability of the existing buildings needs to be evaluated. Since no major damaging earthquake has occurred in Switzerland in recent times, vulnerability functions from observed damage patterns are not available. A simple evaluation method based on engineering models of the building structures suitable for the evaluation of a larger number of buildings is therefore proposed. The method is based on a nonlinear static approach acknowledging the importance of the nonlinear deformation capacity of the buildings subjected to seismic action. Eighty-seven residential buildings in a small target area in Basel were evaluated. The results are vulnerability functions that express the expected damage as a function of the spectral displacement. In order to extrapolate the results to other residential areas of the town, building classes were defined for which the vulnerability is presented in a probabilistic form that can be used directly for earthquake scenario projects.